An 8.65-g sample of an unknown group 2a metal hydroxide is dissolved in 85.0 ml of water. an acid-base indicator is added and the resulting solution is titrated with 2.50 m hcl(aq) solution. the indicator changes color signaling that the equivalence point has been reached after 56.9 ml of the hydrochloric acid solution has been added.

Answer;

The molar mass of metal hydroxide = 121.66 g/ mole

The formula is Sr(OH)2

Explanation;

M(OH)2 + 2 HCl = MCl2 + 2 H2O  

Moles of the acid = 2.5 x 56.9 / 1000 = 0.14225  

Therefore; moles of hydroxide at the eq point = 0.0711 moles  

These have a mass of 8.65g

Thus; mass of 1 mole = 8.65 / 0.0711

         = 121.66 g / mole  

That means the compound is Sr (OH)2 ..